Cured tread and tire

ABSTRACT

The invention provides a cured tread and a tire capable of controlling irregular wear of the tread. A base tire which is to be the base for the tire and a cured tread which is to be bonded to the base tire are molded separately, and they are integrated with each other to produce the tire. The tread is provided in its width (axial) direction with a plurality of grooves extending in its length (circumferential) direction. The thickness of the tread in a width cross section gradually decreases from the equator to the equator-side edge of the outermost groove located at an axially outermost position and gradually increases from the outer edge of the outermost groove outward in the axial direction.

This is a Division of application Ser. No. 14/113,281 filed Oct. 22,2013, which in turn is a National Phase of International PatentApplication No. PCT/JP2012/067675 filed Jul. 11, 2012, which claimspriority to Japanese Patent Application No. 2011-157094 filed Jul. 15,2011. The disclosure of the prior applications are hereby incorporatedby reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to a cured tread and, more particularly,to a cured tread capable of controlling the irregular wear of a tireproduced by separately molding a base tire, which is to be the base forthe tire, and a cured tread, which is to be bonded to the base tire, andintegrating them together, and a tire having the cured tread thereon.

BACKGROUND ART

In one of known methods of tire manufacture, a base tire, which servesas the base for a tire, and a cured tread, which is to be bonded to theouter periphery of the base tire as the tread of the tire, are moldedseparately and then the base tire and the tread are integrated with eachother into a product tire.

A base tire is obtained, for instance, by removing the tread portion ofa used tire with a buffing machine. And the surface after the removal ofthe tread portion is formed as the bonding surface to which a new treadis bonded. The bonding surface is formed in such a way that the cuttingpart of a grinder is brought into contact with the tread portion of aused tire which is mounted fixedly to the drum of a buffing machine withthe internal pressure applied. More specifically, the grinder is movedback and forth repeatedly in the width direction of the used tire whilethe drum is rotated. Thus the bonding surface is formed into apredetermined shape such that the curvature radius in the axial crosssection of the bonding surface is smaller away from the tire axialcenter toward each side. Bonded to the base tire having the bondingsurface of the predetermined shape is a cured tread which has beenformed with a fixed thickness or with a thickness thinner away from theaxial center toward each side. In this manner, a product tire iscompleted with these two parts integrated with each other.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 9-70903

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2001-180228

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, as mentioned above, the bonding surface of the base tire isformed such that the curvature radius becomes smaller away from theaxial center toward each side thereof. Therefore, if a cured treadhaving a fixed thickness or a cured tread thinner from the axial centertoward each side thereof is bonded to the base tire, then the curedtread will bend in an arc in the axial direction. As a result, thegrooves (main grooves) extending in the length (circumferential)direction in the cured tread get stretched in the axial direction suchthat there will be greater radius difference between the inner edge andthe outer edge of each of the grooves.

Especially with the grooves located in outermost positions of the curedtread, the radius difference is greater than that at the edges of theother grooves. Consequently, the ground contact length will becomelonger than assumed at the time of tire design, and irregular wear willbe more likely to occur in the axially outer areas of the tread on theproduct tire on the road. Also, in the forming of the bonding surface ofa base tire, the tread portion of a used tire is buffed while the widthof the bead portions is spread wider than the rim width of a wheel towhich the tire is fitted. Therefore, depending on the aspect ratio ofthe used tire, there may be cases where the shape of the tread surfacewhen the completed product tire is fitted to the wheel is further bentthan the shape of the tread surface at the time of buffing. In suchcases, the radius of the tread toward the axial sides tends to besmaller than the radius of the middle portion of the tread, and theground contact length in the axial sides of the tread can becomeextremely shorter than that assumed at the time of tire design. Thus,this will raise the likelihood of irregular wear in the axially middlearea of the cured tread when the product tire is on the road.

The present invention has been made to solve the above-describedproblems, and an object thereof is to provide a cured tread capable ofcontrolling irregular wear of a tire having a cured tread bonded to thebonding surface of a base tire and a tire having such a cured treadapplied thereto.

Means for Solving the Problem

To solve the above-described problems, a cured tread is so configuredthat it has in its width direction a plurality of grooves extending inits length direction. And the tread thickness in a width cross sectiongradually decreases from the equator to the equator-side edge of theoutermost groove located at an axially outermost position and graduallyincreases from the outer edge of the outermost groove outward in theaxial direction.

According to this configuration, the thickness in the axial crosssection of a cured tread having in its axial direction a plurality ofgrooves extending in the circumferential direction of the treadgradually decreases from the equator to the equator-side edge of theoutermost groove located at an axially outermost position and graduallyincreases from the outer edge of the outermost groove outward in theaxial direction. Accordingly, it is possible to optimize the groundcontact shape of the tread surface of a product tire having the curedtread thereon when it comes in contact with the road surface.

More specifically, the tread thickness in the axial cross section of thetread gradually decreases from the equator to the equator-side edge ofthe outermost groove located at an axially outermost position. As aresult, the sectional shape along the tread surface of a product tirewith the cured tread applied thereto will be a smooth curve when aproper internal pressure is applied therein. Also, the tread thicknessin the axial cross section of the tread gradually increases from theouter edge of the outermost groove outward in the axial direction. As aresult, it is possible to prevent the noncontact with the road surfaceof the part of the tread outside of the outermost groove in the axialdirection. Thus the irregular wear of the tread can be controlledbecause the tread surface of a product tire can be brought into contactwith the road surface in a well-balanced manner.

Also, another cured tread is so configured that it has in its width(axial) direction a plurality of grooves extending in its length(circumferential) direction. And the tread thickness in a width crosssection gradually decreases from the equator to the equator-side edge ofthe outermost groove located at an axially outermost position and isfixed from the outer edge of the outermost groove outward in the axialdirection.

According to this configuration, the thickness in the axial crosssection of a cured tread having in its axial direction a plurality ofgrooves extending in the circumferential direction of the treadgradually decreases from the equator to the equator-side edge of theoutermost groove located at an axially outermost position and is fixedfrom the outer edge of the outermost groove outward in the axialdirection. Accordingly, it is possible to optimize the ground contactshape of the tread surface of a product tire having the cured treadapplied thereto when it comes in contact with the road surface.

More specifically, the tread thickness in the axial cross section of thetread gradually decreases from the equator to the equator-side edge ofthe outermost groove located at an axially outermost position. As aresult, the sectional shape along the tread surface of a product tirewith the cured tread applied thereto will be a smooth curve when aproper internal pressure is applied therein. Also, the tread thicknessin the axial cross section is fixed from the outer edge of the outermostgroove outward in the axial direction. As a result, it is possible toprevent the excessive contact of the axially outermost portion of thetread surface with the road surface. For example, a product tire with atread applied to a base tire which has a lower aspect ratio shows asmaller change in the radius at the outer edge of the axially outermostgroove, when the internal pressure is applied, than a product tire witha tread applied to a base tire which has a higher aspect ratio.Therefore, the tread thickness in the axial cross section from the outeredge of the outermost groove outward in the axial direction being fixedwill prevent an excessive contact or noncontact of the outer edge of theoutermost groove with the road surface. Thus, it is possible to controlthe irregular wear of the tread because the tread surface of the producttire comes in contact with the road surface in a well-balanced manner.

Also, another cured tread is so configured that the tread thickness inthe width cross section at an axially outermost side is thinner than thethickness of the cross section at the equator.

According to this configuration, the tread thickness in the axial crosssection of the tread at an axially outermost side is thinner than thesectional thickness at the equator. As a result, the ground contactlength at the equator along the tire circumference will be the longestwhen a product tire comes in contact with the road surface. Accordingly,the tread of the product tire in contact with the road surface will havean ideal ground contact shape. That is, without the tread scratchingagainst the road surface, the rolling resistance will be smaller andirregular wear will not occur on the tread.

Also, another cured tread is so configured that the tread thickness inthe width cross section at the equator-side edge of the outermost grooveis thicker than the tread thickness at the outer edge of the outermostgroove.

According to this configuration, the tread thickness at the equator-sideedge of the outermost groove is thicker than that at the outer edge ofthe outermost groove. This will provide an edge effect in the axiallyouter area of the tread, thereby improving cornering and stability.

Also, another cured tread is so configured that the tread thickness inthe width cross section at the equator-side edge of the outermost grooveis equal to the tread thickness at the axially outermost side of thetread.

According to this configuration, the tread thickness at the equator-sideedge of the outermost groove is equal to the tread thickness at theaxially outermost side of the tread. Hence, it is possible to preventthe excessive contact of the axially outermost side of the cured treadwhen the product tire comes in contact with the road surface.

Also, another cured tread is so configured that the tread thickness inthe width cross section gradually decreases in a curve from the equatorto the equator-side edge of the outermost groove located at an axiallyoutermost position.

According to this configuration, a tire featuring the performanceassumed at tire design and low rolling resistance causing no irregularwear can be produced.

Also, to solve the previously described problems, a tire is soconfigured that it has thereon any one of the cured treads describedabove.

According to this configuration, the tread surface of the product tirecan be brought into contact with the road surface in a well-balancedmanner, and so irregular wear of the tread of the tire can becontrolled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective illustration of a tire with its tread bonded tothe base tire.

FIG. 1B illustrates an exploded view of a tire with its tread bonded tothe base tire.

FIG. 2A is an appearance perspective illustration of a tread.

FIG. 2B illustrates a cross-sectional view in an axial direction of atread.

FIG. 3 is a plan view of a tread.

FIG. 4 is an enlarged view of a cross section of a tread.

FIG. 5 is a cross-sectional view of another shape of a tread.

FIG. 6A illustrates a sectional shape of a cure-molded tread.

FIG. 6B illustrates a sectional shape of a conventional tread 10 of aflat plate type having a fixed sectional thickness.

FIG. 6C illustrates a ground contact shape of a product tire having atread.

FIG. 6D illustrates a ground contact shape of a tire having aconventional tread.

FIG. 6E provides a table showing the differences in the lengths of theground contact shapes of FIG. 6C and FIG. 6D

FIG. 7A illustrates a sectional shape of a cure-molded tread.

FIG. 7B illustrates a sectional shape of a conventional tread.

FIG. 7C illustrates a ground contact shape of a product tire having atread.

FIG. 7D illustrates a ground contact shape of a tire having aconventional tread.

FIG. 7E provides a table showing the differences in the lengths of theground contact shapes of FIG. 7C and FIG. 7D.

Hereinafter, the invention will be described based on preferredembodiments which do not intend to limit the scope of the claims of thepresent invention but exemplify the invention. All of the features andthe combinations thereof described in the embodiments are notnecessarily essential to the invention, and they include constructionsand arrangements to be employed selectively.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1A is an exploded perspective view of a product tire constructed bybonding a tread 1 according to the present invention to a base tire 2.FIG. 1B is a cross-sectional view of a product tire with the tread 1bonded to the base tire 2 through the medium of a bonding layer 3. FIG.2 is an appearance perspective illustration of a tread 1 and across-sectional view thereof in a width (axial) direction. FIG. 3 is aplan view of a tread 1.

As shown in FIGS. 1A and 1B, a tread 1 according to the presentinvention is bonded through the medium of a bonding layer 3 formed onthe outer periphery of a base tire 2. As shown in FIG. 2, the tread 1 isa tread cure-molded into a strip shape of predetermined dimensions. Thesectional shape of the tread 1 in the width direction is approximatelytrapezoidal with the non-contact surface 1 a side to be bonded to thebase tire 2 formed in a linear fashion and the contact surface 1 b sideto contact with the road surface formed in a wavelike fashion.

Formed in the contact surface 1 b of the tread 1 are a plurality of maingrooves M1 and M2 extending along the length direction when the tread 1is bonded to the base tire 2 and axial grooves N1, N2, N3 axiallyconnecting the adjacent main grooves M1 and M2 with each other or themain grooves M1 and M1 with each other.

The main grooves M1 are located closer to the equator which is the axialcenter of the tread, whereas the main grooves M2 are the outermostgrooves located axially outside of the main grooves M1. Formed on thegroove bottoms of the main grooves M1 and M2 are wear indicatorsindicating the wear limits of the tread 1 (see JIS D 4230) , forinstance.

The axial grooves N1, N2, N3, which have, for instance, the same depthas the main grooves M1 and M2, are formed at regular or irregularintervals along the length direction of the tread. The contact surface 1b of the tread 1 in the present embodiment is comparted into blocks by aplurality of the main grooves M1 and M2 and a plurality of axial groovesN1, N2, N3.

As shown in FIG. 2 and FIG. 3, in the contact surface 1 b which is theside of the tread coming in contact with the road surface, the axialgrooves N1 connecting the main groves M1, M1 with each other are formedat regular or irregular intervals along the circumferential direction ofthe tread. As a result, center blocks 5 defined by the axial grooves N1,N1 are formed in the axially middle area of the tread 1. Also, in thecontact surface 1 b, the axial grooves N2 connecting the main groves Mlwith the main grooves M2 are formed at regular or irregular intervalsalong the circumferential direction of the tread. As a result, sideblocks 6 defined by the axial grooves N2, N2 are formed on the axiallyoutward side of the center blocks 5.

Also, in the contact surface 1 b, the axial grooves N3 connecting themain groves M2 with the tread side surface S (hereinafter referred to asside surface S) are formed at regular or irregular intervals along thecircumferential direction of the tread. As a result, shoulder blocks 7defined by the axial grooves N3, N3 are formed on the axially outwardside of the side blocks 6.

In the present embodiment, the tread pattern is described as beingsymmetrical with respect to the equator P1, which is the tread widthcenter as shown in FIG. 3 and FIG. 4 (hereinafter referred to as theaxial center P1), for simplicity. However, an actual tread pattern isnot limited to this description of the embodiment.

FIG. 4 is an enlarged view of an axial cross section of a tread 1 takenalong line A-A of FIG. 3 . Hereinbelow, a description is given of thethickness in the axial direction of a tread 1 having tread blocks 5, 6,and 7 with reference to FIG. 3 and FIG. 4.

As shown in FIG. 3 and FIG. 4, the center blocks 5 are located in theaxially middle area of the tread 1, straddling the axial center P1 inthe axial direction.

The thickness H2 from the non-contact surface 1 a to the contact surface1 b at the axial center P1 side edge P2 of the main groove M1 definingthe center blocks 5 and the side blocks 6 is set thinner than thethickness H1 from the non-contact surface 1 a to the contact surface 1 bat the tread center P1. The edge P2 is the equator-side edge of the maingroove M1 opening on the contact surface 1 b.

Also, the thickness H3 from the non-contact surface 1 a to the contactsurface 1 b at the axially outer edge P3 of the main groove M1 is formedeven thinner than the thickness H2 at the above-mentioned edge P2. Theedge P3 is the outer edge of the main groove M1 opening on the contactsurface 1 b.

The thickness H4 from the non-contact surface 1 a to the contact surface1 b at the axial center P1 side edge P4 of the main groove M2 definingthe side blocks 6 and the shoulder blocks 7 is formed even thinner thanthe thickness H3 at the above-mentioned edge P3. The edge P4 is theequator-side edge of the main groove M2 opening on the contact surface 1b.

In other words, the tread 1 according to the present embodiment isformed such that in the axial cross section the thickness H1 at theaxial center P1 is the thickest and the thickness becomes graduallythinner in the order of the edges P2, P3, and P4. More specifically,from the axial center P1 to the axial center P1 side edge P4 of the maingroove M2 located in an outermost position, the sectional thickness ofthe tread 1 is so formed as to gradually decrease in the axialdirection.

Thus the thickness of the tread 1 is so formed as to gradually decreasefrom the axial center P1 to the edge P4. As a result, when the tread 1is bonded in a curve along the width of the curved bonding surface ofthe base tire 2, the virtual line connecting the edges P2, p3, and P4 ofthe tread blocks 4 will be a smooth line declining monotonically fromthe axial center P1 to the edge P4. More specifically, with the tread 1bonded to the bonding surface, the edge P2 and the edge P3 of the maingrooves M1 are displaced in the radial direction while moving away fromeach other due to the axial curvature of the bonding surface. Yet, thesurface from the axial center P1 to P3 is smooth without the edge P2 andthe edge P3 sticking out because the thickness of the tread 1 decreasesprogressively and smoothly from the edge P2 to the edge P3. And, withthe thickness gradually decreasing from the axial center P1 to the edgeP2 of the center blocks 5 and from the edge P3 to the edge P4 of theside blocks, the tread surface of a product tire having the tread 1thereon will take a form such that the tread surface smoothly andgradually decline from the axial center P1 to the edge P4.

It is to be noted that the sectional shape line connecting the axialcenter P1 and the edges P2, P3, and P4 is preferably a smooth curveapproximating the buff line, for instance. But the shape of the line maybe such that the line extends in a step-by-step or linear manner withineach of the blocks. Also, the declining rate of the thickness may alsobe set arbitrarily.

Next, a description is given of the sectional thickness of the treadaxially outside of the edge P4.

The thickness H5 from the non-contact surface 1 a to the contact surface1 b at the edge P5 axially outside of the main groove M2 is formed eventhinner than, for example, the thickness H4 at the above-mentioned edgeP4. The edge P5 is the axially outer edge of the main groove M2 openingon the contact surface 1 b. The thickness H6 from the non-contactsurface 1 a to the contact surface 1 b at the edge P6 on the contactsurface 1 b side of the tread side surface S of the tread 1 is so formedas to be thicker than the thickness H at the edge P5. The edge P6 is theaxially outermost edge of the contact surface 1 b where the contactsurface 1 b meets the tread side surface S. That is, the edge P6 is theaxially outermost edge of the ground contact area of the tread 1.

More specifically, the thickness H5 at the edge P5 on the axially outerside of the main groove M2 is formed even thinner than the thickness H4at the edge P4, and the sectional thickness is gradually increased fromthe edge P5 to the axially outermost edge P6 such that the thickness H6at the edge P6 is equal to the thickness H4 at the edge P4.

In other words, the sectional thickness is gradually increased from theedge P5 in such a manner that the thickness H6 at the edge P6 is thesame as the thickness H4 at the edge P4. Also, the line connecting theedge P5 with the edge P6 in the sectional shape is set as a straightline, for instance.

As described above, the thickness H5 at the outer edge P5 of the maingroove M2 is formed even thinner than the thickness H4 at the edge P4.As a result, when the tread 1 is bonded along the curvature of thebonding surface, the surface from the axial center P1 to the edge P5 isformed in a smooth curve without the edge P4 and the edge P5 of the maingroove M2 sticking out.

Also, the tread 1 is formed such that the thickness increases graduallyfrom the outer edge P5 of the main groove M2 located at an axiallyoutermost position to the edge P6 which is the axially outermost edgethereof. As a result, the tread 1 can be bonded to the bonding surfacein an optimal curve from the edge P5 to the edge P6 when it is bondedalong the curve of the shoulder area of the base tire 2 where the changein curvature is marked. That is, the gradual increase in the thicknessfrom the edge P5 to the edge p6 can reduce the difference in radiusbetween the edge P5 and the edge p6 which may likely occur on a producttire due to the marked change in curvature of the bonding surface in theshoulder area of the base tire 2. Also, when the tread 1 is bonded tothe bonding surface, the thickness H6 at the edge P6 being formed equalto the thickness H4 at the edge P4 will ensure that the surface from theedge P4 to the edge P6 via the edge P5 is formed in a smooth curve. Thiswill prevent an excessive contact of the edge P6, which is the axiallyoutermost edge of the contact surface 1 b of the cured tread, when theproduct tire having the tread 1 on comes in contact with the roadsurface.

The tread 1 is formed such that, while maintaining the above-describedrelationship of thicknesses in the axial direction, the sectionalthickness at any given axial position is fixed in the circumferentialdirection thereof. That is, when the tread 1 is axially cut at any givencircumferential position, the shape of the contact surface 1 b remainsthe same.

FIG. 5 is a cross-sectional view showing another shape of the tread 1.In the foregoing embodiment, the sectional thickness of the tread 1 isso formed as to gradually increase from the edge P5 to the edge P6.However, the present embodiment differs in that the sectional thicknessis fixed from the edge P5 to the edge P6.

As shown in FIG. 5, the tread 1 in this embodiment is formed with thesectional thicknesses in the axial direction as follows. The thicknessH1 at the axial center P1 is the thickest, and then the thickness isformed gradually thinner from the edge P2 to the edge P3 to the edge P4.And the thickness H5 at the edge P5 is formed even thinner than thethickness H4 at the edge P4, and the thickness H6 is formed fixed fromthe edge P5 to the edge P6 which is the axially outermost edge. That is,the sectional shape from P5 to P6 is formed in a straight line.

According to the present embodiment, the thickness of the tread 1 fromthe edge P5, which is the edge on the tread side surface S side of themain groove M2 located at an axially outermost position, to the edge P6is so formed as to be fixed. As a result, when it is used for a basetire 2 with a lower aspect ratio, the tread 1 can be bonded to thebonding surface in an optimal curve from the edge P5 to the edge P6along the curve of the shoulder area of the base tire 2 where the changein curvature is marked. In other words, a base tire 2 with a loweraspect ratio shows a smaller change in the curvature of the bondingsurface in the shoulder area, which is located in the axially outermostposition, when the internal pressure is applied, than a base tire 2 witha higher aspect ratio. Therefore, the thickness from the edge P5 to theedge P6 being fixed will create a smooth curve from the edge P5 to theedge P6 when a product tire is manufactured by applying a tread 1 to abase tire 2 with a lower aspect ratio. This will prevent an excessivecontact of the edge P6, which is the axially outermost edge of the tread1 when the product tire comes in contact with the road surface. Thus,the tire having the tread 1 of this embodiment bonded thereto cancontrol the irregular wear of the tread 1 because the contact surface 1b thereof comes in contact with the road surface in a well-balancedmanner.

The tread 1 in each of the foregoing embodiments is molded with apress-type curing machine, for instance.

Although not shown, the curing machine is equipped with a contactsurface side mold for molding the contact surface 1 b side of the tread1 and a non-contact surface side mold for molding the non-contactsurface 1 a side thereof. The machine can receive a tread materialshaped, beforehand in a strip (band) into the molding space defined bythe two molds and heat it under a predetermined pressure.

The surface of the contact surface side mold is formed with a pattern ofraised and recessed portions which is the inversion of the tread patternon the tread 1. Thus, a tread 1 having a desired tread pattern can beproduced when a surface of the tread material is pressed against thesurface of the contact surface side mold. On the other hand, the surfaceof the non-contact surface side mold is formed as a flat surface.Accordingly, the surface of the tread material facing the flat surfacewill be formed as the non-contact surface of the tread 1.

Hereinbelow, an outline will be given of a manufacturing process of aproduct tire in which a tread 1 having sectional thicknesses asdescribed above is bonded to a base tire 2. A base tire 2 as shown inFIG. 1 can be obtained, for instance, by removing the tread portion of aused tire with a not-shown buffing machine. Although not shown, thebuffing machine is equipped with a drum that can hold a used tire withan internal pressure applied and a grinder located in opposition to thedrum and having a cutting part capable of cutting the tread portion ofthe used tire while it is rotated by the drum. The drum, which is acylindrical body consisting of a plurality of drum pieces attachedexpandably and contractably, can fixedly hold a used tire of differingsizes. Also, the drum has flanges along the outer periphery which areaxially spaced apart at a given distance. The flanges, which correspondto the rim flanges of a wheel, secure a pair of bead portions tightlythereon when an internal pressure is applied to the used tire.

The grinder is installed in such a manner that it can move closer to oraway from and axially along the used tire held by the drum. And thegrinder is brought closer to the tread portion of the rotating used tireand the tread portion is removed gradually by moving the cutting part ofthe grinder in contact with the tread portion in the axial direction. Inthis way, a base tire 2 having a bonding surface of a predeterminedshape (buff line) can be produced.

A bonding layer 3 is placed on the bonding surface along thecircumference of the base tire 2 formed through the above-describedprocess. The bonding layer 3, which is an uncured gum called cushiongum, is formed by extruding the gum material into a uniform thicknessonto the bonding surface using an extrusion-molding machine, forinstance.

Now the above-described tread 1 is wound circumferentially around thebonding surface of the base tire 2 having the bonding layer placedthereon.

That is, the tread 1 is provisionally integrated with the base tire 2through the medium of the bonding layer 3. Next, the tread 1 and thebase tire 2 provisionally integrated with each other are placed in asealed bag called an envelope.

The envelope has a valve through which the air inside can be expelled.After the tread 1 and the base tire 2 are placed inside the envelope,the air inside is expelled through the valve so as to bring the theenvelope into close contact with the surfaces of the tread 1 and thebase tire 2. Then the tread 1 and the base tire 2 compressed by theenvelope are carried into a curing unit called a curing can. Inside thecuring unit, the cushion gum as the bonding layer between the tread 1and the base tire 2 will bond the tread 1 and the base tire 2 firmlytogether as curing progresses under a predetermined pressure andtemperature for a given period of time. In this manner, the manufactureof a product tire is completed.

EXAMPLE 1

FIG. 6A shows a sectional shape of a cure-molded tread according to thepresent invention. FIG. 6B shows a sectional shape of a conventionaltread 10 of a flat plate type having a fixed sectional thickness. FIG.6C shows a ground contact shape of a product tire having a tread 1according to this invention applied thereto. FIG. 6D shows a groundcontact shape of a tire having a conventional tread 10 applied thereto.FIG. 6E is a table showing the differences in the lengths of the groundcontact shapes of FIG. 6C and FIG. 6D. It is to be noted that in thetable, the ground contact lengths L4 to L6 at the edges P4 to P6,respectively, are represented by the percentages to the ground contactlength L1 at the tread center P1 along the circumference of the tire asreference (100).

In Example 1, a comparative testing was conducted by preparing basetires 2 by buffing used tires of 275/80R22.5 and manufacturing testproduct tires applying a tread 1 of the present invention on one basetire 2 and a cure-molded tread 10 on the other base tire 2 as acomparative example.

As shown in FIG. 6A, the tread 1α(1) in Example 1 was formed such thatthe width thereof on the non-contact surface 1 a side was 250 mm. Thethickness H1 thereof at the axial center P1 was 18.8 mm, the thicknessH4 at the edge P4 was 18.3 mm, the thickness H5 at the edge P5 was 17.8mm, and the thickness H6 at the edge P6 was 18.3 mm. The sectionalthickness from the axial center P1 to the edge P4 gradually decreased ina curve. The sectional thickness at the edge P5 was set thinner thanthat at the edge P4. The sectional thickness at the edge P6 was setequal to that at the edge P4. And the sectional thickness from the edgeP5 to the edge P6 gradually increased in a linear manner.

As shown in FIG. 6B, the tread 10α(10), which was a comparative example,was formed as a flat plate whose thickness was fixed at 18.8 mm from theaxial center P1 to the edge P6.

Hereinbelow, a description is given of a tire with a tread la bondedthereto as product tire A and a tire with a tread 10 a bonded thereto asproduct tire B.

As shown in FIG. 6C, FIG. 6D, and FIG. 6E, it is evident that producttire A meets the target shape (ground contact lengths) assumed at tiredesign. That is, product tire A having a desired ground contact shapecan be manufactured by molding the tread 1α such that the sectionalthickness of the tread 1α gradually decreases from the axial center P1to the axial center P1 side edge P4 of the main groove M2 located at anaxially outermost position and gradually increases from the outer edgeP5 of the main groove M2 to the axial side thereof. And no irregularwear was observed on product tire A because the contact surface 1 b wasin a desired shape especially in the area axially outside of the maingroove M2 where the diameter change is the greatest when the internalpressure is applied. Thus, product tire A having the tread 1α of thepresent invention applied thereto is a tire featuring the performanceintended at tire design and low rolling resistance without irregularwear.

On the other hand, product tire B tends to have generally longer groundcontact lengths than the target lengths assumed at tire design. Inparticular, the ground contact length L5 at the edge P5 is longer thanthe ground contact length L1 at the axial center P1. That is, producttire B having the tread 10 a bonded thereto turned out to have irregularwear at the edge P5 portion without having a uniform wear on the entiretire tread because the edge P5 was locally pushed hard against the roadsurface. The irregular wear of this type can be a factor in increasingthe rolling resistance, which will cause instability in steering thevehicle.

EXAMPLE 2

FIG. 7A shows a sectional shape of a cure-molded tread 1 according tothe present invention. FIG. 7B shows a sectional shape of a conventionaltread 10 of a flat plate type having a fixed sectional thickness. FIG.7C shows a ground contact shape of a product tire having a tread 1according to this invention applied thereto. FIG. 7D shows a groundcontact shape of a tire having a conventional tread 10 applied thereto.FIG. 7E is a table showing the differences in the lengths of the groundcontact shapes of FIG. 7C and FIG. 7D. It is to be noted that in thetable, the ground contact lengths L4 to L6 at the edges P4 to P6,respectively, are represented by the percentages to the ground contactlength L1 at the tread center P1 along the circumference of the tire asreference (100).

In Example 2, a comparative testing was conducted by preparing basetires 2 by buffing used tires of 11R22.5, a tire size different fromthat of Example 1, and manufacturing test product tires applying a tread1 of the present invention on one base tire 2 and a cure-molded tread 10on the other base tire 2 as a comparative example.

As shown in FIG. 7A, the tread 1β(1) in Example 2 was formed such thatthe width thereof on the non-contact surface 1 a side was 230 mm. Thethickness H1 thereof at the tread center P1 was 18.8 mm, the thicknessH4 at the edge P4 was 18.3 mm, the thickness H5 at the edge P5 was 17.8mm, and the thickness H6 at the edge P6 was 17.8 mm. The sectionalthickness from the axial center P1 to the edge P4 gradually decreased ina curve. The sectional thickness at the edge P5 was set thinner thanthat at the edge P4. The sectional thickness at the edge P6 was setequal to that at the edge P4. And the sectional thickness from the edgeP5 to the edge P6 was so formed as to be fixed.

As shown in FIG. 7B, the tread 10β(10), which was a comparative example,was formed as a flat plate whose thickness was fixed at 18.8 mm from theaxial center P1 to the edge P6.

Hereinbelow, a description is given of a tire with a tread 1β bondedthereto as product tire A and a tire with a tread 10β bonded thereto asproduct tire B.

As shown in FIG. 7C, FIG. 7D, and FIG. 7E, it is evident that producttire A meets the target shape (ground contact lengths) assumed at tiredesign. That is, product tire A having a desired ground contact shapecan be manufactured by molding the tread 4 such that the sectionalthickness of the tread 4 gradually decreases from the axial center P1 tothe axial center P1 side edge P4 of the main groove M2 located at anaxially outermost position and is fixed from the outer edge P5 of themain groove M2 to the edge P6, which is the axially outermost edge. Theproduct tire A of this Example, in particular, has a high aspect ratioin comparison with the product tire A of Example 1. Therefore, theproduct tire A of this Example, formed to have a fixed thickness fromthe outer edge P5 of the main groove M2 to the axial side, showed noirregular wear because the contact surface 1 b took a desired shape inthe area axially outside of the main groove M2 subject to the greatesttire diameter change when the internal pressure is applied. Accordingly,product tire A having the tread 1β of the present invention appliedthereto is a tire featuring the performance intended at tire design andlow rolling resistance without irregular wear.

On the other hand, product tire B, which has a higher aspect ratio thanthat of the product tire B of Example 1, tends to have longer groundcontact lengths in the axially outer area of the tread 10β than thetarget lengths assumed at tire design. In particular, the ground contactlength L6 at the edge P6 is much longer than the target length. That is,product tire B having the tread 10β bonded thereto turned out to haveirregular wear especially at the edge P6 without having a uniform wearon the entire tire tread because the shoulder blocks 7 were pushed hardagainst the road surface. The irregular wear of this type can be afactor in increasing the rolling resistance, which will causeinstability in steering the vehicle.

As hereinbefore described, irregular wear of the tread 1 on a producttire can be prevented by employing the sectional thickness of the tread1β gradually decreasing from the axial center P1 to the axial center P1side edge P4 of the main groove M2 located at an axially outermostposition and gradually increasing or being fixed from the outer edge P5of the main groove M2 to the edge P6, which is the axially outermostedge, depending on the aspect ratio of the tire. That is, when theaspect ratio of the base tire is low, the thickness H6 from the outeredge P5 of the main groove M2 to the edge P6, which is the axiallyoutermost edge, is gradually increased. And when the aspect ratio of thebase tire is low, the thickness H6 from the outer edge P5 of the maingroove M2 to the edge P6, which is the axially outermost edge, is fixed.In this manner, it is possible to prevent irregular wear of the tread1β.

Also, the thickness H5 at the edge P5 may be set equal to or thickerthan the thickness H4 at the edge P4 as appropriate. This will providean edge effect in the axially outer area, or the tire shoulder area,thereby improving the cornering performance and stability of thevehicle.

In the foregoing embodiments, the tread 1 has been described as beingformed in a strip (band) shape. Yet the tread 1 is not limited to astrip shape, but may be an annular tread which has been cure-molded intoa ring shape in advance.

Also, in the foregoing embodiments, the base tire has been described asone formed by buffing the worn tread portion of a used tire. But thebase tire may be a newly produced base tire cure-molded and then formedby buffing the crown portion thereof.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. However, the technical scopeof this invention is not to be considered as limited to thoseembodiments. It will be evident to those skilled in the art that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the invention. It will also be evident fromthe scope of the appended claims that all such modifications areintended to be included within the technical scope of this invention.

DESCRIPTION OF REFERENCE NUMERALS

1, 1α, 1β tread

1 a non-contact surface

1 b contact surface

2 base tire

3 bonding layer

4 tread block

5 center block

6 side block

7 shoulder block

H1-H6 thickness

L1, L4, L5, L6 ground contact length

M1, M2 main groove

N1, N2, N3 axial groove

P1 tread center

P2-P6 edge

1. A cured tread having in a width direction thereof a plurality ofgrooves extending in a length direction thereof, wherein tread thicknessin a width cross section gradually decreases from an equator to anequator-side edge of an outermost groove located at an outermostposition in the width direction and is fixed from an outer edge of theoutermost groove outward in the width direction.
 2. A cured treadaccording to claim 1, wherein the tread thickness in the width crosssection at the equator-side edge of the outermost groove is equal to thetread thickness at the outermost side of the tread.